It is known to provide printheads having driver circuits for driving actuating elements to eject fluid from an actuating chamber in inkjet printers. Existing piezoelectric (‘piezo’) cold switch driver ASICs have the limitation of the cost and power dissipation of the high voltage pass gates and associated level shifter used to gate a cold switch power waveform on to each individual actuating element. One problem is how to provide electrical drive for a piezo actuating element at the lowest cost and with the lowest power dissipation while still meeting minimum drive requirements.
The inkjet industry has been working intensively on how to drive piezoelectric actuating elements for more than twenty years. Multiple drive methods have been produced and there are multiple different types in use today. Some are briefly discussed now.
Hot Switch: This is the class of driving methods that keep the demux function and the power dissipation (CV^2) in the same driver IC (Integrated Circuit). This was the original drive method, before cold switch became popular.
Rectangular Hot Switch: This describes hot switch systems that have no flexible control over rise and fall time and only two voltages (0V and 30V for example). In some cases waveform delivery is uniform to all the actuating elements. The waveform has some level of programmability.
DAC Hot Switch describes a class of drive options that has a logic driving an arbitrary digital value stream to a DAC (Digital Analog Converter) per actuating element, and outputs a high voltage drive power waveform scaled from this digital stream. In terms of driving flexibility, this option has the most capability. It is limited only by the number of digital gates and the complexity that that system designers can use and/or tolerate.
Cold Switch Demux: This describes an arrangement in which all actuating elements are fed the same drive signal through a pass gate type demultiplexer. The drive signal is gated at sub-pixel speeds.
It is also known to provide some factory calibration of differences between individual actuating elements and to provide compensation by trimming the drive signal applied to the different actuating elements. Patent application US20130321507 shows compensating for actuating element variations by altering rise times of drive pulses for individual actuating elements and thus alters the properties of an ejected droplet. The ejection rate is altered by changing an amount of series resistance or an internal resistance of a drive circuit.
It is known from US20120262512A1 to provide a cold switched arrangement using a common drive waveform switched to provide a drive signal for each actuating element. The highest voltage and the lowest voltage of the drive signal or the basic shape of the waveform of the drive signal can be changed by changing the timing of switching. This can be used to correct for variations between the actuating elements.